Shaped rubber compositions containing petroleum cresylic acid monosulfides



SHAPED RUBBER COMPOSITIONS CONTAINING PETROLEUM CRESYLIC ACIDMONOSULFIDES Harry E. Albert, Akron, Ohio, and Lloyd 0. Bentz, .Lan-

caster, Pa., assignors to The Firestone Tire & Rubber Company, Akron,Ohio, a corporation of Ohio No Drawing. Application December 24, 1953Serial No. 400,342

2 Claims. (Cl. 260-810) This invention relates to the use of cresylicacid sultides in natural rubber compositions to prevent attack of therubber by ozone. Sulfides of coal tar cresylic acids are notparticularly effective, and disclor white stocks. The cresylic acidsulfides to which this invention relates are monosulfides of cresylicacids derived from petroleum, and they are sulfides of only thosecresylic acids which boil above 195 C., and preferably those boiling nohigher than 250 C., although those boiling up to 300 C. are active to amore limited extent. These cresylic acids are non-discoloring. They aresubstantially free from phenol and may contain some cresols, asubstantial amount of dialkylphenols and also a high percentage oftrialkylphenols.

The cresylic acids are converted to monosulfides by reacting with SClThe monosulfide obtained by reacting 1 mole of SCl with 2 moles of acresylic acid is preferred, although the reaction product obtained byusing up to 1.5 moles of SCl is satisfactory.

The petroleum cresylic acids are very different in composition from thecoal tar cresylic acids. The latter are not suitable for the purposes ofthis invention. They contain different isomers from the petroleumcresylic acids, and different ratios of the same isomers.

Oxygen and ozone both have a harmful effect on rubher, but the effect ofeach is different, and compounds which inhibit or prevent the harmfuleffect of one are not necessarily effective in stopping the harmfuleffect of the other.

Crabtree and Kemp in an article in Industrial and Engineering Chemistry,vol. 38, starting at page 278 (1946) explain the difference in theaction of oxygen and ozone. The light-catalyzed oxidation which occursduring outdoor exposure forms a skin and crazed appearance over theexposed surface of the rubber. Ozone, even in very low concentration,attacks stretched rubber only (C. H. Leigh-Dugmore, Rubber Age andSynthetics, November and December, 1952), and forms cracks perpendicularto the direction of stretch, and such cracking can occur in the absenceof light.

As a matter of fact, practically all commercial rubber antioxidants arewithout effect in inhibiting deterioration caused by ozone. The cresylicacid monosulfides of this invention do not absorb or act directly on theozone, but have some unknown action in preventing the cracking which isassociated with ozone exposure in stretched natural rubber.

Natural rubber is used in the manufacture of the whitesidewalls oftires. long been a problem. It is often very extensive, and because ofthe color of the sidewall, it is very noticeable. It is a primary objectof this invention to provide antiozone agents which prevent suchcracking without discoloring the sidewall. However, the antiozone agentsof this invention are not limited to that use but may be employed inblack sidewalls, treads, thread and other latex products, and otherrubber products.

ited States Patent The cracking of such sidewalls has Tires are stressedwhen inflated. While a tire is at rest it is stretched statically, andona moving vehicle it is stretched dynamically, and this is particularlytrue of the sidewalls. Some of the antiozone agents are more effectivein static tests and others are more effective in dynamic tests.Antiozone agents effective under both conditions will be desired fortires, but for other rubber products an antiozone agent which does notmeet both tests may be used.

The inhibiting effect of the cresylic acid sulfides of this inventionwas determined by treatment of rubber compositions with air ofcontrolled low ozone content in specially designed equipment and also byoutdoor exposture to natural weathering. The tests were conducted withone-half inch dumbbell samples of approximately gauge thickness. Thespecial apparatus and method of testing are described in the articles byFord and Cooper, appearing in India Rubber World for September andOctober, 1951, entitled A Study of the Factors Affecting the Weatheringof Rubber-Like Materials1 and II. In the following reports the ozoneconcentration maintained during each test is given in parts per100,000,000 parts of air. The length of exposure to this ozone and thetemperature used are also given. Two types of tests were conducted. Inone type, called the dynamic test, the sample was repeatedly stretchedbetween the limits of 0 and 20 percent elongation at the rate of 108cycles per minute. In the other type of test, the static test, thesamples were stretched at 12.5 percent elongation throughout theexposure. No special lights were used. On completion of each test thesize of the cracks in each sample was compared visually with the size ofthe cracks in a blank which contained no antiozone agent and which wascured and tested at the same time as the test sample. An arbitrary scaleof measuring the results was adopted using the numerals 0, 1, 2, 3, 4and 5 to represent no visual cracking and cracks which were very fine,fine, medium, coarse and very coarse, respectively.

The reported results include data on the tensile properties of the curedrubber stocks. The modulus and tensile strength are given in pounds persquare inch and the elongation is reported as percent of stretch at thebreak. These properties are reported for cured unaged vulcanizate aswell as for vulcanizate which was aged two days in an oven at 212 F.

The antiozone agents were tested in white stock such as might be used inthe white sidewalls for tires. The blanks of the white stock werecompounded according to the following formula:

Parts by weight Natural rubber 100 White pigment and filler 90.2 Stearicacid 1.2 Sulfur 3Z0 Accelerator 0.9

Total 195.3

cresylic acid sulfide may be employed, and this may vary,

for example, from 0.2 part by weight to 10 parts by weight, dependingupon the use to be made of the rubber composition.

Specifications are given for several petroleum cresylic acids,illustrative of those that may be employed. The specifications are eachfollowed by instructions for preparing the sulfides used in the testsdescribed below. Two sulfides were prepared from each of the first threeacids, one using a slight excess over the ratio of 2 parts acid to 1part SCl and the other using 50 percent excess sulfur chloride, or aratio of 2 parts acid to 1.5 parts SCl Petroleum cresylic acidmonosulfide N 0. 1A

This petroleum cresylic acid has a boiling range of 193 to 226 C.

Preparation of sulfide-A monosulfide was prepared from 24.4 g. of thecresylic acid in 100 ml. n-hexane plus 50 ml. ethylene dichloride, and10.8 g. SCl This yielded 26.1 g. of a clear, black, viscous liquid.

Petroleum cresylic acid monosulfide No. 1B

The petroleum cresylic acid monosulfide of higher sulfur content wasprepared by the reaction of 24.4 g. of the foregoing petroleum cresylicacid dissolved in 100 ml. .n-hexane and 50 ml. ethylene dichloride, with15.5 g. SCI This gave 28 g. of black, viscous, tacky solid.

Petroleum cresylic acid monosulfide N 0. 2A

This petroleum cresylic acid has a boiling range of 248 to 300+ C. Thesupplier gives these further specifications:

Specific gravity at 60 F 1.020 Sulfur, percent by Weight 0.16Distillation, C.:

I. B. P 248 251 50% 262 95% 297 E. P f 300+ Neutral oil, percent byvolume -1 0.4 maximum Solid matter None C alkyl phenols, percent byweight, the

balance being principally higher alkyl phenols 75-80 Preparation ofsulfide.A monosulfide was prepared by allowing 30.0 g. (0.2 mole) of thecresylic acid to react With 10.8 (0.105 mole) SCl in 100 ml. of n-hexaneand 50 ml. of ethylene dichloride. Thirty one and a half grams of ablack, sticky resin was obtained.

Petroleum cresylic acid monosulfide No. 2B

The preparation of this monosulfide was identical with the foregoingexcept that 15.5 g. (0.15 mole) SCl was employed. The yield was 33.5 g.of a black resin.

Petroleum cresylic acid monosulfide N 0. 3A

This petroleum cresylic acid has a boiling range of 221 to 245 C. Thesupplier gives these further specifications:

Specific gravity at 60 F. 1.013 Sulfur, percent by weight 0.08Distillation, C.:

I. B. P 221 5% 223 50% 227 95% 241 E. P 245 Neutral oil, percent byvolume 0.4 maximum Solid matter None Xylenols, percent by weight 8-10 Calkylphenols, percent by weight 45-55 C; alkyl phenols, percent byweight 30-40 Preparation of sulfide.A solution of 27.2 g. of cresylicacid in 200 ml. of .n-hexane and 100 ml. of ethylene dichloride wasprepared and 10.8 g. of sulfur dichloride was added at 25 to 30 C. overa half-hour period. Removal of the solvent gave 29.0 grams of a viscousbrown liquid.

Petroleum cresylic acid monosulfia'e N 0. 3B

Twenty-seven and two tenths grams (0.2 mole) of the foregoing cresylicacid in 100 ml. n-hexane and 50 ml. ethylene dichloride were allowed toreact with 15.5 g. (0.105 mole) SO1 This yielded 32.8 g. of brown,sticky resin.

Petroleum cresylic acid monosulfide N o. 4

This petroleum cresylic acid had a boiling range of 217 to 240 C.

Preparation of sulfide.-Twenty-seven and two tenths grams (0.2 mole) ofthe cresylic acid was dissolved in 100 ml. n-hexane and 50 ml. ethylenedichloride and allowed to react with 10.8 g. (0.105 mole) SCI The yieldwas 28.5 g. of brown viscous liquid.

Petroleum cresylic acid monosulfide No.5

This petroleum cresylic acid has a boiling range of 246 to 271 C.

Preparation of sulfide.A solution of 30.0 g. (0.2 mole) of the cresylicacid in 100 ml. n-hexane and 50 ml. ethylene dichloride was allowed toreact with 10.8 g. (0.105 mole) SCI This yielded 33.8 g. black, veryviscous liquid.

Petroleum cresylic acid monosulfide N o. 6

This petroleum cresylic acid has a boiling range of 200 to 228 C. Thesupplier gives these further specifications:

Specific gravity at 100 F 1.032 Sulfur, percent by Weight 0.37Distillation, C.:

I. B. P 200 F. B. P 228 Neutral oil, percent by weight 0.4 Mercaptansulfur, percent by weight 0.27 Phenol constituents, percent by weight:

Phenol 1 o-Cresol 9-11 m-Cresol 4-5 p-Cresol 4-5 Xylenols 25-35 C alkylphenols 38-42 C alkyl phenols 0 Preparation of sulfide.-The monosulfidewas prepared by the reaction of 10.8 g. (0.105 mole) SO1 with a solutionof 24.4 g. of the cresylic acid in ml. n-hexane and 50 ml. ethylenedichloride.

Tables 1 and 2 show the results of tests conducted with certain of theforegoing cresylic acid monosulfides in white stock. Tables 3, 4 and 5record the results of further tests in white stocks, comparingmonosulfides of different sulfur contents derived from the same cresylicacids, as aforesaid.

TABLE l-WHITE STOCK Blank 195. 3 195. 3 195. 3 Oresylic acid monosulfideN o. 2.0 Cresylic acid monosulfide N0. 5 2. 0 Normal tensile properties:

400% modulus 975 925 1,050

Tensile strength 3, 700 3, 550 3, 625

Elongation at break 625 620 595 Aged 2 days in oven at 212 F;

400% modulus 625 950 Tensile strength 1, 725 2, 250 2, 025

Elongation at break 560 540 510 01 1 effects (7 hrs. at 60 p. p. h. m.and 95 Static 4+ 1 22 Dynamic 4 1 TABLE 2-WHITE STOCK Blank 195.3 195.3195. 8 Cresylic acid monosulfide N 0. 3A 2.0 Cresylic acid monosulfideNo. 1A 2.0 Normal tensile properties:

400% modulus 925 875 900 Tensile strength... 3, 400 3, 425 3, 525Elongation at; break. 610 61 615 Aged 2 days in oven at 212 F.:

400% modulus 87 975 900 Tensile strength--. 2, 325 2, 300 2, 125Elongation at break 545 545 540 Ozlgne eflects (7 hrs. at 60 p. p. h. m.and 95 Static 4 2 1+ Dynamic 4+ 2- 1+ ofiaone effects (4 hrs. at 45 p.p. h. m. and 95 TABLE 3-WHITE STOCK Blank 195. 3 195. 3 195. 3 Oresylicacid monosulfide N 0. 1A 2.0 Cresylic acid monosulfide N 0. 1B 2.0Normal tensile properties:

400% modulus 875 9 850 Tensile strength 3, 275 3, 425 3, 425 Elongationat break 610 610 630 Aged 2 days in oven at 212 F 400% modulus. 1, 0251, 000 975 Tensile strength 2, 625 2,275 2, 175 Elongation at bre 530525 530 zFo1)1e effects (7 hrs. at 60 p. p. h. m

Static 4- 1 1+ Dynamic 4- 1- 1 TABLE 4-WHIIE STOCK Blank 195.3 195. 3195.3 Cresylic acid monosulfide N 0. 2A 2. 0 Oresylic acid monosulfide No. 2 2.0 Normal tensile properties:

400% modulus 900 900 925 Tensile strength.-- 3, 725 3, 425 3, 450Elongation at break 660 615 620 Aged 2 days in oven at 212 F.:

400% modulus 750 925 950 Tensile strength 1, 376 1, 900 1, 800Elongation at break 495 505 495 Ozone efiects (7 hrs. at 60 p. p. h. m.and 95 TABLE 5-WHI'IE STOCK Blank 195. 3 195. 3 195. 3 Cresyllc acidmonosulfide No. 3A. 2. 0 Cresylic acid monosulflde No. 3B 2. 0 Normaltensile properties:

400% modulus 1, 000 1, 075 1, 025 Tensile strength--. 3, 625 3, 315 3,515 Elongation at break 62 590 610 Aged 2 days in oven at 400% modulus.825 1, 075 1, 025 Tensile strength 2, 025 2, 400 2, 250 Elongation athrs 54 540 540 Cagney eflects (7 hrs. at 60 p. p I

fltaflr- 4 0+ 1- Dynamic 4- 1 1- The following. table records theresults of exposing white stocks to natural Weathering.

TABLE 6-EVALUATION OF WHITE STOCKS AFTER OUTDOOR EXPOSURE The recordedresults are illustrative. They show that the cresylic acid monosulfidesof this invention prevent or inhibit the deterioration caused by ozone.They may be used in rubber compositions compounded for use in rubberthread and in other rubber stocks.

By sulfur vulcanization is meant the curing of rubber by reaction witheither free sulfur or a vulcanizing agent of the sulfur-donor type.Known agents of the latter type include the various phenol polysulfidesincluding the alkyl derivatives thereof, the zanthogen polysulfides, thethiuram disulfides and polysulfides, various amine sulfides includingdialkylamine polysulfides and reaction products of primary amines withexcess sulfur. Known vulcanization accelerators are useful in speedingup the vulcanization process and are operative herein, especially therelatively active accelerators including the thiazole sulfenamides, e.g. N-cycloheXyl-Z-benzothiazolesulfenamide, thiazoline sulfenamides,thiocarbamyl sulfenamides, mercaptothiazoles, mercaptothiazolines,thiazoyl monoand di-sulfides, the N,N-dialkyl-dithiocarbamates, thethiuram sulfides, the Xanthogen sulfides, metallic salts ofmercaptothiazoles or rnercaptothiazolines or dithiocarbamic acids. Oneor more accelerator activator is often used with any of the acceleratorsmentioned, and such activators include the various derivatives ofguanidine known in the rubber art, amine salts of inorganic and organicacids, various amines themselves, alkaline salts such as sodium acetateand the like, as well as other activators known to the art.Additionally, two or more accelerators or accelerator,combinations aresometimes desirable in a single rubber compound. Many of theaccelerators mentioned above are suitable in latex formulations,especially such common accelerators as piperidiniumpentamethylene-dithiocarbarnate, zinc butylxanthate, zinc ethylxanthate,zinc salt of mercaptobenzothiazole, zinc dimethyldithiocarbamate, andzinc dibutyldithiocarbamate. Although vulcanization is usuallyaccomplished by heating a vulcanizable rubber composition at atemperature in the range of 240 to 400 F. for a time ranging fromseveral hours to a few seconds, vulcanization does take place at lowertemperatures such as ordinary room temperature. It is quite common tovulcanize a latex film containing an ultra accelerator by allowing thefilm to remain at room temperature for several hours or a few days.

What is claimed is:

1. A white, shaped, sulfur-vulcanized composition of natural rubberwhich is adapted to be stretched dynamically, contains sufficient whitepigment to make the composition white and contains as a non-discoloringantiozone agent, a small amount of monosulfide of a cresylic acid ofpetroleum origin which 1) is substantially free from phenol and (2)contains monoalkylphenols, dialkylphenols and trialkylphenols and (3)boils above C. and no higher than 250 C.

2. A white, shaped, sulfur-vulcanized composition of natural rubberwhich is adapted to be stretched dynamically, contains sufiicient whitepigment to make the composition white and contains as a non-discoloringantiozone agent, a small amount of monosulfide of a cresylic acid ofpetroleum origin which is composed largely of alkyl phenols containing atotal of no less than three carbon atoms in the alkyl substitutents, thecresylic acid boiling between 195 C. and 250 C.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Cook et al., Ind. and Chem, vol. 40, No.

7, pp. 1194-1202, July 1948.

UNITED STATES PAIAENT OFFICE CERTIFICATE OF CORRECTION Patent N0".2,849,516 August 26, 1958 Harry E. Albert et a1 It is hereby certifiedthat error appears in the printed specification of the above numberedpatent requiring correction and that the said Letters Patent shouldreadas corrected below.

Column 2, lines 13 and 14, for "expostur'e" read exposure c'olumn 4,Table 1, last column thereof, for that portion of the column reading;

read 22 2- Signed and sealed this 26th day of April 1960..

(SEAL) Attest:

KARL H. ,mrmz ROBERT C. WATSON Attesting Officer Commissioner of Patents

1. A WHITE, SHAPED, SULFUR-VULCANIZED COMPOSITION OF NATURAL RUBBERWHICH IS ADAPTED TO BE STRETCHED DYNAMICALLY, CONTAINS SUFFICIENT WHITEPIGMENT TO MAKE THE COMPOSITION WHITE AND CONTAINS AS A NON-DISCOLORINGANTIOZONE AGENT; A SMALL AMOUNT OF MONOSULFIDE OF A CRESYLIC ACID OFPETROLEUM ORIGIN WHICH (1) IS SUBSTANTIALLY FREE FROM PHENOL AND (2)CONTAINS MONOALKYLPHENOLS, DIALKYLPHENOLS AND TRIALKYLPHENOLS AND (3)BOILS ABOVE 195* C. AND NO HIGHER THAN 250*C.